JPH0650269B2 - Pressure transducer for low pressure measurement - Google Patents

Description

TECHNICAL FIELD The present invention relates to pressure transducers, and more particularly to liquid ring pressure transducers such as the pressure transducers of the type disclosed in US Pat. Nos. 3,349,623 and 3,678,753. The invention more particularly relates to low pressure range pressure transducers.

Technical Background As described in the above U.S. patents, liquid ring pressure transducers are designed for use in systems where it is undesirable for the medium whose pressure is to be measured to penetrate into the transducer. . In this case, the transducer itself encloses a liquid, which is operatively coupled via a diaphragm or other device with the medium to be measured. The liquid enclosed in the transducer transmits the pressure of the medium to be measured directly to the sensor device. A typical liquid is mercury.

U.S. Pat. No. 3,678,753 discloses a pressure transducer that includes an extension frame and a capillary tube that extends through the frame and terminates at an end adjacent one end of the frame. The coupler seals the end of the frame and cooperates with the frame to form a chamber that communicates with the capillaries. The other end of the capillary communicates with the sensor device, which has little deflection over the entire working range. The sensor device is in the form of a flexible cap member having a recess therein and cooperates with a portion of the frame to form a disc-shaped, thin sensor compartment in communication with the capillary. A liquid, preferably mercury, fills the thin-walled sensor compartment, said chamber and the capillary, whereby the pressure exerted on the coupler is transmitted directly to the sensor device to measure the pressure.

This pressure transducer is generally designed for pressures above 1500 p.si. 1500 with this prior art converter
To measure pressures below psi, the flexible walls or diaphragms of the cap members are too thin to be difficult to manufacture and easy to break.

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved liquid ring pressure transducer particularly suitable for measuring low pressures, such as in the range 250-1500 p.si. More particularly, the present invention is capable of performing pressure measurements in this low pressure range without the use of large components. Especially in the present invention, the standard 1/2 inch-20
It is possible to measure in the low pressure range using a threaded nozzle on the mountain.

It is another object of the present invention to provide an improved low pressure range measuring pressure transducer that is relatively simple in construction and relatively inexpensive to manufacture.

It is a further object of the invention to provide an improved method of constructing a sensor device.

It is another object of the present invention to provide an improved low pressure range measuring pressure transducer having a structure that reduces the tensile force generated in the diaphragm portion to reduce the non-linearity of the diaphragm.

It is an object of the invention to provide an improved low pressure range measuring pressure transducer, generally the same as that disclosed in U.S. Pat. No. 3,678,753, but having shaped dents on either side of the raised beam. It is another object of the present invention. The dents here reduce the tensile forces generated within the diaphragm with the beam, so that the beam is free to bend and reduce the non-linear properties of the diaphragm.

SUMMARY OF THE INVENTION In order to achieve the above objects, features and advantages of the present invention, an extension frame, particularly for pressure measurement in the low pressure range, having an extension passage therein, and an extension frame extending therethrough opposite the frame. A pressure transducer is provided that comprises a capillary terminating in a side end and a coupler that seals the other end of the frame and forms a chamber communicating with one end of the capillary. The liquid ring flexible sensor has a cap member having an internal recess in the top wall. The recess forms a thin disk-shaped compartment at the other end of the frame,
The discoid chamber communicates with the other end of the capillary via a liquid. Liquid fills the capillaries, chambers, and compartments, and the liquid transfers the pressure exerted on the coupler to the sensor. According to the invention, the cap member has an outer top surface formed by the cap member top wall forming a thin walled diaphragm, having a raised beam diametrically extending transversely on the top surface. It has a gauge mounting surface on the top. Strain gauge means can be attached to the gauge mounting surface of the beam. In the preferred embodiment,
A plurality of strain gauges are provided longitudinally along the beam. 2 for compressive strain measurement, 2 for tensile strain measurement
It is preferable to provide a total of four strain gauges. The beam preferably extends over the entire width of the cap member and has a constant width along it. In an alternative aspect of the invention, the beam may have a flared end. The thickness of the beam is preferably at least about twice the wall thickness of the thin diaphragm wall.

In another aspect of the invention, the top surface of the cap member has recesses therein on opposite sides of the raised beam. These adjacently located dents serve to allow the beam to flex freely and reduce the tensile forces generated in the diaphragm as the beam flexes. The more free movement of the beam reduces the non-linearity of deflection throughout the beamed diaphragm.

It has been found that when a beam is constructed by the construction method of the present invention, the surface is simply shaved off based on the flat diaphragm surface disclosed in US Pat. No. 3,678,753 to form the beam as designed. The top wall portion of the cap member is cut or cut so that the thickness of the beam is about 2 times that of the adjacent thin film.
It has been found that it is preferable to carry out doubling. It was further found that when the beam was formed starting from the cap in the pressure range R and the beam was formed, the measured pressure range of the device changed to R / 4. In an alternative embodiment, a longitudinally extending recess is then formed by stamping on the flat top surface of the relatively thin cap member, adjacent to and on both sides of the raised beam. According to a preferred alternative of the invention, the indentation is stamped from the outside. However, in a preferred alternative of the present invention, the indentation may be stamped from inside the cap member.

Various objects, features and advantages of the present invention will become apparent from the following detailed description of the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, and in particular to FIG. 1, FIG. 1 shows a sectional view of a pressure transducer according to the invention, which comprises a main frame 10 and a sensor part 1 provided at the top end of the frame.
2, a capillary tube 14 extending through the frame, and a diaphragm coupler 16 attached to the closed bottom end of the frame. The lower portion of frame 10 may have a structure similar to that described in US Pat. No. 3,678,753. The main frame is provided with an elongate passageway 18 for extending therethrough to accommodate the capillary tube 14 therein. The bottom end of the capillary 14 terminates in a relatively small chamber 20 that is sealed by a diaphragm 16.

The top end of the frame 10 is provided with a top piece 22 as part of the frame in which the capillary tube 14 extends. The top part 22 is for supporting the sensor part 12 in the position shown. The sensor component 12 may be welded to the top component 22.

The sensor component 12 shown in FIG. 1 includes a bottom portion 26 and a cap member 30. The cap member 30 is welded to the bottom portion 26, and a thin disk-shaped compartment 32 is formed in the middle thereof.
FIG. 1 also shows fill tube 34 and accessory fill plug 36. The filling tube 34 communicates with the thin disk-shaped compartment 32. The filling liquid in the device that fills the chamber 20, the compartment 32 and the capillary 14 is introduced under pressure from the filling pipe 34, so that all areas are completely filled with mercury. The tube 34 is then sealed with a plug 36.

2-4 show the sensor component 12 in more detail, the sensor component 12 having a bottom 26 and a cap member 30. The cap member 30 is shown in FIGS.
As shown in the figure, the welded portion 35 is welded to the bottom portion 26. In this regard, FIG. 2 also shows an annular weld line 35. FIG. 3 shows a disk-shaped compartment similar to FIG. It can be seen in FIGS. 3 and 4 that the top end of the capillary is shown as terminating directly in the thin disk compartment 32. 3 and 4 also show that the top of the capillary 14 is welded at the weld 37 to the top surface 33 of the bottom 26 itself.

The cap member 30 now has an outer top surface formed by the cap member top wall 40 forming a thin diaphragm. A diametrically raised ridge beam 42 is provided integrally with the wall 40,
2 has an upper gauge mounting surface 44 extending transversely to the top surface. The diaphragm acts as a force recovery part for amplifying the force transmitted to the beam. This makes the beam thicker and the eighth
As shown in the figure, it becomes possible to show an appropriate linear characteristic.

The sensor diaphragm formed by the cap member with beam 30 provides a structure operable in the low pressure range, particularly in the range of 250, 500, 750, 1000, and 1500 p.si. In this construction, it is possible to reduce the rigidity of the diaphragm 40 and make the beam section thicker than the generally flat diaphragm used in the same pressure range. For example, in the range of 750p.si, the thickness of the beam is
While 0.0177 inches, the diaphragm for the same pressure range has a thickness of 0.0100 inches, which is too thin to break easily and has no linearity. In this regard, Table I (see below)
Please refer to.

5A and 5B also show only cap member 30. Particularly in FIG. 5B, the dimensions T1 and T2 are shown. The dimension T1 is the thickness of the beam 42, while the dimension T2 is the thickness of the diaphragm 40. It has been found that the relationship between these dimensions is preferably within a certain range. It is preferable that the thickness of the diaphragm 40 be as thin as possible, but if it is too thin, there is a problem that it is easily damaged. It is preferable that the thickness of the beam 42 is as thick as possible, but if it is too thick, the sensitivity of the device will decrease. It has been found that the ratio T1 / T2 is preferably about 2. This is shown in FIGS. 3 and 5B, in which the cut-off portion shown in FIG. 3 originally cuts off the original cap member whose top surface is completely flat to a half depth. The thickness of the diaphragm 40 is about half that of the beam 42.

See Table I below for dimensions T1 and T2.

As an example, for a pressure range of 250 p.si, the dimension T1 is
The range is 0.0099 / 0.0104 inches, and the dimension T2 is 0.0044 /
It is in the range of 0.0050. Taking the average value of each range, T1 / T2
The ratio is 2.18.

In another example, for the 1000p.si range, the dimension T1 is 0.0220.
/0.0226, and the dimension T2 is 0.0100 / 0.0110. Here again, taking the average value of each dimension, the ratio of T1 / T2 is 1.92. The T1 / T2 ratio is preferably between 1.5 and 4.0.

As described above, the beam 42 has an upper gauge mounting surface 44. Regarding this, it can be seen that FIGS. 2 and 4 show four strain gauges G1-G4. Each of these strain gauges may be of conventional design and may be of the "D" alloy foil material type. The gauge resistance is 350 ohms.
Figure 6 shows the arrangement of strain gauges.
The individual gauges are arranged along the beam 42 of the cap member 30. Gauges G1 and G4 measure compressive force, while gauges G1 and G4
2, G3 measures the tensile force. Thus, gauges G1 and G4 measure negative induced strain, while gauges G2 and G3 measure positive induced strain. It can be seen that the gauges G2 and G3 are arranged symmetrically with respect to the center of the cap member and at a slight interval. The gauges G1 and G4 are arranged on the same line as the gauges G2 and G3 in the longitudinal direction. Gauge G1 is spaced from gauge G2 and gauge G4 is spaced from gauge G3 as shown in FIG.

Gauges G1-G4 are connected by a circuit as shown in FIG.
R1-R4 in FIG. 7 correspond to gauges G1-G4, respectively.

In FIG. 6, gauges G1-G4 are connected as in the circuit of FIG. In this connection, the conductive contacts C1, C2, C3 are provided on one side of the beam 42, or the contacts C4-C6 are provided on the other side of the beam 42.
Is provided. A conductor couples between the strain gauge and electrical contacts C1-C6. In this case also, the coupling conductor forms a circuit as shown in FIG.

FIG. 7 shows a gauge coupled to a bridge structure, the bridge having a pair of input terminals coupled to one end of the bridge,
And a pair of output terminals drawn from the other end of the bridge. An input signal is input between the input terminals and a voltage corresponding to the pressure is measured between the output terminals.

In FIG. 1 above it was shown that the bottom end of the capillary tube 14 terminates in a relatively small chamber 20 sealed by a septum 16. However, in the preferred embodiment of the present invention, a fill member 70 as shown in FIG. 1A is provided. In this regard, FIG. 1A shows an enlarged cross-sectional view of the preferred embodiment of the device tube end, which is provided with a tube end filling member 70 used primarily for temperature compensation. The filling member is preferably made of Kovar or Invar. Alternatively, it may be made of another very low expansion coefficient material. It preferably has a coefficient of expansion much lower than that of the stainless steel frame. This filling member enables the space in the chamber 20 to expand at the same rate as the liquid even if the temperature changes. Filling member 70 shown in FIG. 1A.
Acts to reduce the internal fill pressure that occurs when the tip is heated without pressure.

Thus, the fill member cooperates with the chamber 20 shown in FIG. 1A to provide a preferred thermal compensating internal volume. Said filling member also has a thermal property such that it makes a temperature compensation for the converter with respect to the difference in the coefficient of thermal expansion between the internal liquid, preferably mercury, and the main body of the converter, where usually stainless steel is used. Are selected to have. As mentioned above, the filling member preferably has a coefficient of thermal expansion lower than that of the frame material.

FIG. 8 shows the characteristic curve between input pressure (% of its full scale) and non-linearity (% of its full scale). Two curves C1 and C2 are shown in FIG.
It can be seen that curve C1 corresponds to a standard diaphragm, and exhibits typical non-linearities during operation. Curve C2 corresponds to the structure of the present invention. Desirable linear characteristic for curve C2 (zero access)
It can be seen that there is little variation from.

It will be appreciated that in the preferred embodiment of the present invention, the beam 42 extends symmetrically from edge to edge in the diametrical direction of the sensor component. FIG. 9 illustrates another embodiment, in which beam 42 has flared ends, and thus a central portion 42A of generally constant width in the longitudinal direction and flared ends 42B on either side. This structure also exhibits an operation similar to C2 in FIG. In the embodiment of FIG. 9, only a plan view is shown,
The wall forming the beam is basically an upright wall.

For the coupler diaphragm 16, it is preferable to use a substantially thick planar machined coupler diaphragm in addition to the temperature compensating Kovar filling member. The thicker processed diaphragms, compared to thinly molded and welded conventional diaphragms, are more robust and exhibit a flat surface to the measurement medium. The use of a mercury filling liquid reduces the displacement and thus allows the diaphragm to be thickened.

Mercury is the preferred liquid for filling the device when the converter described herein is used in the temperature range up to about 750 ° F. Mercury has a low compressibility and its boiling point is about 370.
C. (about 700.degree. F.) or higher, and therefore within this working range, secondary expansion of the compartment 32 occurs and the cap member 30
It does not create a vapor pressure that twists the walls 40 and beams 42 of the. An alternative fill liquid that can be used in the device of the present invention is potassium sodium tartrate known as NaK state liquid. This is also liquid.

10 to 20 show another embodiment of the present invention, and the reference numerals use the same numbers for the portions corresponding to those of FIGS. 1 to 9. Also, FIGS. 10, 18, 19, and 20 correspond to FIGS. 1, 6, 7, and 8, respectively, and therefore their description is omitted to avoid duplication.

This embodiment relates to the cap member 30, and more particularly to the cap member top wall 40, which is provided with indentations on opposite sides of a longitudinally extending raised beam 42. In this regard, see FIGS. 11-14 and 16 which illustrate longitudinally extending recesses 50, 52. FIG. 12 shows the extension of these dents.
Figures 11 to 14 also show the shape of the indentation and the extent of its length. These indentations extend only the major portion of the beam that overlies the discoid compartment 32. This relationship is shown in FIG.

The cross-sectional view of Figure 13 shows the position of the beamed diaphragm when unstressed. On the other hand, FIG. 14 shows the beam-attached diaphragm when pressure is applied from the liquid medium as indicated by arrow 54. This causes bending of the beam-attached diaphragm. 14th
As shown, these indentations are curvilinear so that it is possible to impart some bending to the wall 40 to expand or contract the web wall 40 without creating tension in the diaphragm. The presence of these indentations reduces the tensile forces generated on the diaphragm as the beam flexes and attempts to flex more freely. Furthermore, this reduces diaphragm non-linearity throughout the sensing operation.

FIG. 17 shows still another preferred embodiment of the present invention. FIG. 17 differs from the examples shown in FIGS. 13 and 14 in that the recesses are formed from the inside of the cap member 30 like the recesses 60 and 62. These indentations thus actually extend outward as far as the outer surface of the diaphragm is concerned. However, due to these dents, as well,
The bend area prevents the web (wall 40) from being subjected to tensile forces. If tension is applied to the wall 40, it will be non-linear. This non-linearity is a function of this tensile force. By providing a bend region such as by a dent shape, the web can be expanded or contracted without generating a tensile force in the web or the wall 40.

In both of the embodiments shown here, the depressions are preferably extended as a single continuous depression shape on both sides of the beam, and the depressions are preferably as close as possible to the beam. This is clearly illustrated in FIGS. 13 and 17, with the indentation in both figures starting from the immediate crease on the side of the beam. Regarding this, the position of the dent can be seen from the plan views shown in FIGS. 16 and 18.

Although the invention has been described with reference to several embodiments above, it will be apparent to those skilled in the art that numerous other embodiments and modifications are possible within the scope of the invention as claimed. is there.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an embodiment of a liquid ring pressure converter constructed according to the principle of the present invention, and FIG. 1A is an enlarged cross-sectional view of a part of the pressure converter showing a further use of a tube end filling member. 2 is a perspective view of the sensor component shown in FIG. 1, FIG. 3 is an enlarged sectional view of the sensor component shown in FIG. 1, and FIG. 4 is a further enlarged detailed view of the sensor component. Another cross-sectional view along line 4-4 in FIG. 1, FIGS. 5A and 5B are a plan view and a cross-sectional view of a cap member having an integral beam, and FIG. 6 is a sensor showing a strain gauge position and a connection terminal. FIG. 7 is a schematic wiring diagram of the components, FIG. 7 is a schematic circuit diagram showing the strain gauge circuit of FIG. 6, and FIG. 8 is a diagram showing an improved linear characteristic of the input pressure and nonlinearity provided by the transducer of the present invention. Fig. 9 is a graph showing the relationship, and Fig. 9 shows another example of the beam structure in which the beam has a flared end. FIG. 10 is a sectional view of another embodiment of the liquid ring pressure transducer constructed according to the principle of the present invention, FIG. 11 is a perspective view of the sensor component shown in FIG. 10, and FIG. FIG. 12 is an enlarged cross-sectional view of the sensor component also shown in FIG. 1, taken along line 12-12, and FIG. 13 is a cross-section taken along line 13-13 in FIG. 12 showing the beam and indentations located on opposite sides of the beam. Figure 14, Figure 14 is a cross-sectional view similar to Figure 13 but showing the membrane stressed, Figure 15 showing the membrane stressed, taken along line 15-15 in Figure 14. FIG. 16 is a plan view of a cap member according to the present invention showing a beam and a recess provided adjacent it forming a flexible diaphragm, FIG. 17 is similar to FIG. 13, but the recess is a cap. FIG. 18 is a sectional view of another embodiment formed from the inside of the member, FIG. 18 shows strain gauge positions and connection terminals. Fig. 19 is a connection plan view of a sensor component, Fig. 19 is a schematic circuit diagram showing the strain gauge circuit of Fig. 18; and Fig. 20 is a diagram showing the improved linear characteristic provided by the transducer of the present invention. It is a figure which shows the relationship with linearity. 12 ... Sensor parts, 32 ... compartment, 40 ... top wall (flexible wall), 42 ... raised beam, G1, G2, G3, G4 ... gauge.

Claims (11)

[Claims] 1. An elongated frame (10) having a passage, a capillary (14) having an end that passes through the passage of the frame and ends near one end of the frame, and the other end of the frame is closed to remove the other capillaries. Room (2
Sensor (1) having a thin disk-shaped compartment (32) attached to the one end of the frame and communicating with the one end of the capillary.
2) and a liquid for filling the capillary, the chamber, and the thin disk-shaped compartment with liquid for transmitting the pressure applied to the coupler to the sensor, wherein the sensor has a thin disk shape. It has a flexible wall (40) that displaces in response to pressure in the compartment, and has a raised beam (42) integral with its outer surface that extends generally transversely to the center of the outer surface. For low pressure measurement, characterized in that it has a plurality of strain gauges (G1-G4) linearly formed on the surface of the raised beam and spaced apart from each other in the longitudinal direction thereof. converter. 2. The pressure transducer according to claim 1, wherein the flexible wall is substantially flat. 3. The pressure transducer according to claim 1, wherein the beam has a constant width over substantially the entire length thereof. 4. The pressure transducer according to claim 3, wherein the beam has flare ends whose width is wide at both ends thereof. 5. The pressure transducer according to claim 1, wherein the flexible wall has recesses on both sides of the beam. 6. The pressure transducer according to claim 5, wherein the indentation is formed on the outer surface of the flexible wall. 7. The pressure transducer according to claim 5, wherein the indentation is formed on the inner surface of the flexible wall. 8. The pressure transducer according to claim 5, wherein the indentation extends along the beam. 9. Four of the gauges are attached, two of which (G2, G3) are for tensile force and the other two (G2, G3).
The pressure transducer according to any one of claims 1 to 8, characterized in that (1, G4) can be applied with a compressive force. 10. A beam according to claim 1, wherein the thickness of the beam is at least about twice the thickness of the flexible wall. Pressure transducer. 11. When the thickness of the beam is T1 and the thickness of the flexible wall is T2, T1 / T2 is about 1.5 to 4. The pressure transducer according to any one of the first to ninth ranges.